Thomas E. Menke, M.D.
Osteoporosis is a systemic skeletal disease characterized
by decreased bone mass and altered bone structure which leads to
increased fragility of bones and susceptibility to fractures. The
National Osteoporosis Foundation estimates that more than 10 million
people in the United States have osteoporosis and an additional
19 million have low bone mass while not meeting criteria of osteoporosis.
Bone is a living matrix constantly remodeling in response to the
mechanical stresses placed upon it and to the chemical/hormonal
changes of the body. Bone mass increases during childhood, and peak
bone mass is obtained on average by age 25. After this peak, bone
loss occurs at a rate of 0.3% per year for men and 0.5% per year
for women. The rate of bone loss increases to 2% - 3% per year at
the onset of menopause.
The rate of bone turnover is dependent on the surface area of the
ossified bone. Trabecular bone, which is found in the vertebra and
the ends of long bones, has a much greater surface area than cortical
bone. For this reason, osteoporosis causes the most significant
bone density loss in trabecular bone. That is why fragility fractures
most commonly occur in the spine, hip, and distal radius.
Risk factors for the development of osteoporosis include
early menopause, prolonged periods of amenorrhea, poor nutrition,
limited exercise, positive family history, a history of excessive
alcohol intake and smoking. Bone marrow abnormalities, endocrinopathies,
and long-term administration of corticosteroids can also lead to
so-called “secondary osteoporosis.”
Diagnosis of osteoporosis is based on identifying patients
with bone mineral density of 2.5 standard deviations less than the
average value for healthy young adults. The study of choice for
this assessment is dual-energy x-ray absorptiometry (a.k.a. DEXA
scan). DEXA scan offers the best combination of precision, low radiation
exposure, and affordability when compared with other available tests.
Indications for performing a DEXA scan on a patient are still evolving,
but include an assessment of risk factors, family history, and personal
history of any fragility fractures.
Prevention is clearly the best solution to the problem of
osteoporosis. Most people who develop osteoporosis likely never
attained a normal bone mass as a young adult. Diet and exercise
are the two most important reasons. Calcium requirements of 1,000
mg./day (up to 1,500-2,000 mg./day during pregnancy and lactation)
are frequently not fulfilled. This can easily be corrected with
diet changes or supplements.
Exercise, ideally in the form of brisk walking, is beneficial at
all ages. In the extreme, however, it can be very detrimental. Extreme
physical training in adolescent females is often associated with
disordered eating and amenorrhea which leads to low bone mass. As
a group, women who exercise and maintain normal menstrual cycles
have the greatest bone mass. Eumenorrheic women who do not exercise
have less bone mass, and amenorrheic women who exercise have the
least. Female athletes who participate in gymnastics, diving, figure
skating, dance, track, and synchronized swimming appear to be at
the most risk.
Treatment for osteoporosis consists of exercise, most commonly
in the form of a walking program, modification of the environment
to reduce the risk of falls, and medications. Calcium supplements
are beneficial only when a patient’s dietary intake is inadequate.
Excess intake of calcium affords no benefit and can be harmful.
Vitamin D deficiency occurs most commonly in strict vegetarians
and in northern locations during the winter. A single high dose
injection of Vitamin D in early winter has shown signs of being
beneficial for these people.
Estrogen administration to postmenopausal women has clearly been
shown to prevent bone loss and protect against fragility fractures.
Side effects of periodic bleeding, and concern from increased risk
of endometrial and breast cancer, has lead to acceptance of long-term
use of estrogen by only one-third of those women started on it.
Calcitonin administered by injection and, more recently, intranasally
is an alternative to estrogen therapy. In addition to maintenance
of bone density, calcitonin has an analgesic property as a result
of elevating levels of endorphins.
Bisphosphonates such as etidronate and alendronate work by directly
inhibiting bone resorption, but can cause some indigestion.
Flouride decreases bone resorption, but has shown a dose related
abnormality in bone mineralization which has limited its use.
Medications used to treat osteoporosis tend to cause multiple side
effects. Their effectiveness is influenced by other disease processes
and other medications. For these reasons, medical treatment of osteoporosis
is generally managed by one’s primary care physician.
Fractures from osteoporosis cause significant morbidity. Hip fractures
almost always require surgical treatment. Vertebral fractures usually
respond to comfort measures of rest, bracing, and medications. New
procedures (ie. vertebroplasty) are being developed to try to decrease
the morbidity associated with vertebral fractures of moderate severity.
Rarely, osteoporotic vertebral fractures require more aggressive